1. Field
This invention relates to stage lighting systems and, more particularly, to the means for focusing such systems.
2. Prior Art
The prior art system of FIG. 1 comprises a light source formed of two carbon arc elements 101 and 102, a condenser lens system formed of lenses 106 and 107, adjustable iris 105 and objective lens 108.
In the operation of this system, the light passes from the source through the condenser lenses, the iris, and finally the objective lens as shown by light rays 109 and 110. The lenses 106 and 107 are fixedly connected by link 103 and moved together, closer to farther away from the light source and the iris opening is moved in or out with the movement of the condenser lens by means of the linkage 104, however, the location of the iris remains fixed with respect to the light source.
The condenser lenses in this system unfortunately dissipated approximately 40 percent of the light and the arc lamp requires an appreciable area making this equipment inefficient and large.
The components in the system shown in FIG. 2 are similar to those in FIG. 1 and each component that is similar has the same last digit in both figures. The difference between the system of FIG. 2 and that of FIG. 1 is that in FIG. 2, the iris and the objective lens move rather than the condenser lens. This system also uses condenser lens and an arc lamp source and is therefore similarly large and inefficient.
The system in FIG. 3 eliminates the condenser lenses and substitutes a reflector 311. Two lenses 308 and 310 in the objective lens system are moved for focusing. This system is known as the variable focal length system. The objective lens in this system is typically 11 inches in diameter and weighs four pounds. Although the efficiency is higher than the systems shown in FIGS. 1 and 2 because of the use of the reflector in place of the condenser lens, this lamp suffers from imbalance because of the movement of the large and heavy objective lens system, and from large size because of the use of an arc lamp source.